Microelectromechanical gyroscope with open loop reading device and control method

ABSTRACT

A microelectromechanical gyroscope that includes a first mass oscillatable according to a first axis; an inertial sensor, including a second mass, drawn along by the first mass and constrained so as to oscillate according to a second axis, in response to a rotation of the gyroscope; a driving device coupled to the first mass so as to form a feedback control loop and configured to maintain the first mass in oscillation at a resonance frequency; and an open-loop reading device coupled to the inertial sensor for detecting displacements of the second mass according to the second axis. The driving device includes a read signal generator for supplying to the inertial sensor at least one read signal having the form of a square-wave signal of amplitude that sinusoidally varies with the resonance frequency.

BACKGROUND

1. Technical Field

The present disclosure relates to a microelectromechanical gyroscopewith open-loop reading device and a control method for amicroelectromechanical gyroscope.

2. Description of the Related Art

As is known, the use of microelectromechanical systems (MEMS) haswitnessed an ever-increasing diffusion in various sectors of technologyand has yielded encouraging results especially in the production ofinertial sensors, microintegrated gyroscopes, and electromechanicaloscillators for a wide range of applications.

MEMS of the above type are usually based upon microelectromechanicalstructures that comprise at least one mass, which is connected to afixed body (stator) by springs and is movable with respect to the statoraccording to pre-determined degrees of freedom. The movable mass and thestator are capacitively coupled through a plurality of respectivecomb-fingered and mutually facing electrodes so as to form capacitors.The movement of the movable mass with respect to the stator, for exampleon account of application of an external force, modifies the capacitanceof the capacitors, whence it is possible to trace back to the relativedisplacement of the movable mass with respect to the fixed body andhence to the applied force. Vice versa, by supplying appropriate biasingvoltages, it is possible to apply an electrostatic force on the movablemass to set it in motion. In addition, in order to obtainelectromechanical oscillators, the frequency response of inertial MEMSstructures is exploited, which typically is of a second-order low-passtype, with a resonance frequency. By way of example, FIGS. 1 and 2 showthe plot of the magnitude and phase of the transfer function between theforce applied on the movable mass and its displacement with respect tothe stator in an inertial MEMS structure.

In particular, MEMS gyroscopes have a more complex electromechanicalstructure, which includes two masses that are movable with respect tothe stator and coupled to one another so as to have a relative degree offreedom. The two movable masses are both capacitively coupled to thestator. One of the masses is dedicated to driving and is kept inoscillation at the resonance frequency. The other mass is drawn along inoscillating motion and, in the case of rotation of the microstructurewith respect to a pre-determined gyroscopic axis with an angularvelocity, is subjected to a Coriolis force proportional to the angularvelocity itself. In practice, the driven mass operates as anaccelerometer that enables detection of the Coriolis force andacceleration and hence makes it possible to trace back to the angularvelocity.

To operate properly, a MEMS gyroscope requires, in addition to themicrostructure, a driving device, which has the task of maintaining themovable mass in oscillation at the resonance frequency, and a device forreading the displacements of the driven mass, according to the relativedegree of freedom of the driving mass. Said displacements, in fact, areindicative of the Coriolis force and consequently of the angularvelocity, and are detectable through electrical read signals correlatedto the variations of the capacitive coupling between the driven mass andthe stator. As a result of driving at the resonance frequency, the readsignals, determined by the rotation of the gyroscope and correlated tothe angular velocity, are in the form ofdual-side-band-suppressed-carrier (DSB-SC) signals; the carrier is inthis case the velocity of oscillation of the driving mass and has thesame frequency as the mechanical resonance frequency.

Known reading devices detect the read signals at terminals coupled tothe driven mass and demodulate them downstream of the sensing point tobring them back into base band. It is hence necessary to includepurposely provided devices, among which at least one demodulator and asynchronization device, such as for example a PLL circuit, whichgenerates a demodulation signal starting from actuation signals for thedriving mass. The need to include these devices entails, however,disadvantages, principally because it causes a greater encumbrance andincreases the power consumption, which, as is known, is extremelyimportant in modern electronic devices. In addition, the synchronizationdevices must be specifically designed for generating also ahigh-frequency clock signal for the demodulator and are thusparticularly complex.

BRIEF SUMMARY

The present disclosure provides a microelectromechanical gyroscope and amethod for controlling a microelectromechanical gyroscope that will befree from the limitations described.

In accordance with one embodiment of the present disclosure, amicroelectromechanical gyroscope is provided that includes a first massoscillatable according to a first axis; an inertial sensor, including asecond mass, drawn along by the first mass and constrained so as tooscillate according to a second axis in response to a rotation of thegyroscope; a driving device coupled to the first mass so as to form afeedback control loop and configured to maintain the first mass inoscillation at a resonance frequency; an open-loop reading devicecoupled to the inertial sensor and adapted to detect displacements ofthe second mass according to the second axis; and a read signalgenerator adapted to supply to the inertial sensor at least one readsignal having the form of a square-wave signal of amplitude thatsinusoidally varies with the resonance frequency. In accordance withanother embodiment of the present disclosure, a method for controlling amicroelectromechanical gyroscope is provided, the method including thesteps of providing a first mass, oscillatable according to a first axis;coupling an inertial sensor having a second mass to the first mass sothat the second mass is drawn along by the first mass and oscillatesaccording to a second axis in response to a rotation of the gyroscope;feedback controlling a movement of the first mass to maintain the firstmass in oscillation at a resonance frequency; and open-loop detectingdisplacements of the second mass according to the second axis; whereinthe step of open-loop detecting includes supplying to the inertialsensor at least one read signal having the form of a square-wave signalof amplitude that sinusoidally varies at the resonance frequency.

In accordance with another embodiment of the present disclosure, acircuit is provided for use with a first mass and a second mass coupledto the first mass to oscillate in response to the first mass and inresponse to movement of the device, the device including a drivingcircuit coupled to the first mass to form a feedback control loop tomaintain the first mass in oscillation at a resonance frequency; areading device coupled to the second mass and adapted to detectdisplacements of the second mass; and a read signal generator adapted tosupply to the second mass at least one read signal having the form of asquare-wave signal of amplitude that sinusoidally varies with theresonance frequency.

In accordance with another embodiment of the present disclosure, asystem is provided, the system including a control unit; and amicroelectromechanical gyroscope that includes a first mass oscillatableaccording to a first axis an inertial sensor, including a second mass,drawn along by the first mass and constrained so as to oscillateaccording to a second axis in response to a rotation of the gyroscope; adriving device coupled to the first mass so as to form a feedbackcontrol loop and configured to maintain the first mass in oscillation ata resonance frequency; an open-loop reading device coupled to theinertial sensor and adapted to detect displacements of the second massaccording to the second axis; and a read signal generator adapted tosupply to the inertial sensor at least one read signal having the formof a square-wave signal of amplitude that sinusoidally varies with theresonance frequency.

BRIEF DESCRIPTION OF THE SEVERAL VIEWS OF THE DRAWINGS

For a better understanding of the embodiments of the present disclosure,some embodiments thereof are now described purely by way of non-limitingexample and with reference to the attached drawings, wherein:

FIGS. 1 and 2 show graphs of the frequency response of amicroelectromechanical gyroscope;

FIG. 3 is a simplified block diagram of a microelectromechanicalgyroscope according to a first embodiment of the present disclosure;

FIG. 4 is a more detailed block diagram of the microelectromechanicalgyroscope of FIG. 3;

FIG. 5 is a graph that illustrates quantities regarding themicroelectromechanical gyroscope of FIG. 3;

FIG. 6 is a block diagram of a microelectromechanical gyroscopeaccording to a second embodiment of the present disclosure;

FIGS. 7 a and 7 b are graphs that illustrate quantities regarding themicroelectromechanical gyroscope of FIG. 6; and

FIG. 8 is a simplified block diagram of an electronic systemincorporating a microelectromechanical gyroscope according to thepresent disclosure.

DETAILED DESCRIPTION

In the sequel of the description, reference will be made to the use ofthe disclosure in a microelectromechanical gyroscope of the “yaw” type.This is not, however, to be considered in any way limiting, since thedisclosure may advantageously be exploited for the fabrication of MEMSgyroscopes of any type, in particular of the “roll” type, “pitch” typeand with multiple axes (biaxial or triaxial gyroscopes).

For reasons of convenience, moreover, the term “frequency” will be usedto indicate angular frequencies (pulsations, rad/s). It is understood inany case that a frequency f and the corresponding angular frequency orpulsation w are linked by the well-known relation ω=2πf.

A microelectromechanical gyroscope 100, illustrated in a simplified wayin the block diagram of FIG. 3, comprises a microstructure 102, made byMEMS technology, a driving device 103 and a reading device 104, housedon a support 101. The microstructure 102, for example of the typedescribed in EP-A-1 253 399, filed in the name of the present applicant,is provided with an actuation system 5 and an inertial sensor 6,including respective movable masses made of semiconductor material. Moreprecisely, the actuation system 5 includes a driving mass 107,oscillating about a resting position according to a degree of freedom,in particular along a first axis X. The actuation system 5 is moreoverprovided with read outputs 5 a (defined by two stator terminals), fordetecting displacements of the driving mass 107 along the first axis X,and with actuation inputs 5 b (defined by two further stator terminals),for issuing actuation signals and maintaining the driving mass 107 inoscillation at the resonance frequency ω_(R), in a known way. The readoutputs 5 a and the actuation inputs 5 b are capacitively coupled to thedriving mass 107 in a known way, by comb-fingered electrodes (notillustrated herein). The inertial sensor 6 has a detection axis havingthe same direction as a second axis Y perpendicular to the first axis Xand includes a detection mass 108, mechanically connected to the drivingmass 107 by springs (not illustrated herein) so as to be drawn along thefirst axis X when the driving mass 107 is excited. In addition, thedetection mass 108 is relatively movable with respect to the drivingmass 107 in the direction of the second axis Y and hence has a furtherdegree of freedom. A first terminal 6 a (directly connected to thedetection mass 108) and two second (stator) terminals 6 b of theinertial sensor 6 enable, respectively, issuing of a read signal V_(S)to the detection mass 108 and detection of the displacements thereof.The first terminal 6 a is directly connected to the detection masses108, whereas the second terminals 6 b are capacitively coupled theretoin a known way, through comb-fingered electrodes (not illustratedherein).

The driving device 103 is connected to the microstructure 102 so as toform a driving feedback loop 105, including the driving mass 107. Aswill be more fully clarified in the sequel of the description, thedriving device 103 exploits the driving feedback loop 105 to maintainthe driving mass 107 in self-oscillation along the first axis X at itsmechanical resonance frequency ω_(R) (for example, 25 krad/s).

The reading device 104 is of the open-loop type and, in the embodimentdescribed herein, is configured for executing a so-called “double-ended”reading of the displacements of the detection mass 108 along the secondaxis Y. In particular, the reading device 104 has: a first input 104 a,connected to the driving device 103 for acquiring a demodulation signalV_(DEM) (in this case a voltage); second inputs, connected to respectivesecond terminals 6 b of the inertial sensor 6; a first output, connectedto the first terminal 6 a of the inertial sensor 6 and issuing the readsignal V_(S); and a second output 104 b, which supplies an output signalS_(OUT), correlated to the angular velocity Ω of the microstructure 102.

The gyroscope 100 operates in the way hereinafter described. The drivingmass 107 is set in oscillation along the first axis X by the drivingdevice 103. For this purpose, the driving device 103 is coupled to theread outputs 5 a of the actuation system 5 for receiving detectioncurrents I_(RD1), I_(RD2), which are correlated to the linear velocityof oscillation of the driving mass 107 along the first axis X. On thebasis of the detection currents I_(RD1), I_(RD2) the driving device 103generates feedback driving voltages V_(FBD1), V_(FBD2) having amplitudeand phase such as to ensure the conditions of oscillation of the drivingfeedback loop 105 (unit loop gain and substantially zero phase).

The detection mass 108 is drawn in motion along the first axis X by thedriving mass 107. Consequently, when the microstructure 102 rotatesabout a gyroscopic axis perpendicular to the plane of the axes X, Y witha given instantaneous angular velocity, the detection mass 108 issubjected to a Coriolis force, which is parallel to the second axis Yand is proportional to the instantaneous angular velocity of themicrostructure 102 and to the linear velocity of the two masses 107, 108along the first axis X. More precisely, the Coriolis force (F_(C)) isgiven by the equation:F_(C)=2M_(S)ΩX′where M_(S) is the value of the detection mass 108, Ω is the angularvelocity of the microstructure 102, and X′ is the linear velocity of thetwo masses 107, 108 along the first axis X. As a result of driving atthe resonance frequency ω_(R), the detection signals, determined by therotation of the gyroscope and correlated to the angular velocity, are inthe form of dual-side-band-suppressed-carrier (DSB-SC) signals; thecarrier is in this case the oscillation velocity of the driving mass andhas a frequency equal to the mechanical resonance frequency ω_(R).

In effect, also the driving mass 107 is subjected to a Coriolis force;however, this force is countered by the constraints that impose upon thedriving mass 107 movement exclusively along the first axis X.

The Coriolis force and acceleration, which the detection mass 108 issubjected to, are read through the inertial sensor 6. In response to theexcitation of the detection mass 108 by means of the read signal V_(S),the inertial sensor 6 issues differential detection charge packetsQ_(RS1), Q_(RS2), which are proportional to the capacitive unbalancingcaused by the displacement of the detection mass 108 along the secondaxis Y. The detection charge packets Q_(RS1), Q_(RS2) are hencecorrelated to the Coriolis force (and acceleration) and to theinstantaneous angular velocity Ω of the microstructure 102. Moreprecisely, the charge transferred with the detection charge packetsQ_(RS1), Q_(RS2) in successive reading cycles is amplitude modulated ina way proportional to the instantaneous angular velocity Ω of themicrostructure 102. The frequency band associated to the modulatingquantity, i.e., the instantaneous angular velocity, is, however, farlower than the resonance frequency ω_(R) (for example, approximately 30rad/s). The detection charge packets Q_(RS1), Q_(RS2) are converted andprocessed by the reading device 104, which generates the output signalS_(OUT), as explained hereinafter.

FIG. 4 shows a more detailed diagram of the microstructure 102, of thedriving device 103, and of the reading device 104.

As regards the microstructure 102, FIG. 4 shows: first differentialdetection capacitances 120 present between the driving mass 107 andrespective read outputs 5 a of the actuation system 5; actuationcapacitances 121, which are present between the driving mass 107 andrespective actuation inputs 5 b of the actuation system 5; and seconddetection capacitances 122, which are present between the detection mass108 and the second terminals 6 b of the inertial sensor 6. Moreprecisely, the first differential detection capacitances 120 and thedifferential actuation capacitances 121 have respective terminalsconnected to a same actuation node 125, which is in turn coupled to theactuation mass 108.

The driving device 103 comprises a transimpedance amplifier 110, afeedback stage 111, in itself known, and a subtractor circuit 112. Thetransimpedance amplifier 110 is of a fully-differential type and has apair of inputs connected to the read outputs 5 a of the actuation system5 for receiving the detection currents I_(RD1), I_(RD2), which arecorrelated to the linear velocity of oscillation of the driving mass 107along the first axis X. On the outputs of the transimpedance amplifier110 detection voltages V_(RD1), V_(RD2) are hence present, which arealso indicative of the linear velocity of oscillation of the drivingmass 107 along the first axis X. Also the detection voltages V_(RD1),V_(RD2) are sinusoidal, oscillate at the resonance frequency ω_(R), haveequal amplitude, and are 180° out of phase. The conditions of resonanceare ensured by the feedback stage 111, which generates the feedbackdriving voltages V_(FBD1), V_(FBD2) so that the gain of the drivingfeedback loop 105 is a unitary gain and its phase is zero. Thesubtractor circuit 112 has inputs connected to the outputs of thetransimpedance amplifier 110, for receiving the detection voltagesV_(RD1), V_(RD2). The output of the subtractor circuit 112 is connectedto the first input 104 a of the reading device 104 and supplies thedemodulation signal V_(DEM) (see also FIG. 5). Also the demodulationsignal V_(DEM) is sinusoidal and oscillates at the resonance frequencyω_(R), because it is generated as a difference between the detectionvoltages V_(RD1), V_(RD2). In addition, given that the detectionvoltages V_(RD1), V_(RD2) are differential voltages 180° out of phase,the demodulation voltage V_(DEM) has a higher absolute value as comparedto that of the detection voltages.

The reading device 104 includes a read signal generator 130, a phasegenerator 131 and, moreover, a fully differential processing line 132including a charge amplifier 133, a preamplifier 134, and a sampler 135.

The read signal generator 130 is a sampler and has a clock input,connected to the phase generator 131 for receiving a clock signal CK(with clock period T_(CK)), and an input forming the first input 104 aof the reading circuit 104.

The clock signal CK is asynchronous with respect to the oscillation ofthe driving mass 107 (in practice, the clock frequency 2π/T_(C) is notcorrelated to the resonance frequency ω_(R)). Also the sampling carriedout by the read signal generator 130 is hence asynchronous with respectto the resonance frequency ω_(R). The output of the read signalgenerator 130 is connected to a first terminal 6 a of the inertialsensor 6 and supplies the read signal V_(S).

The charge amplifier 133 has inputs connected to respective secondterminals 6 b of the inertial sensor 6 for receiving the detectioncharge packets Q_(RS1), Q_(RS2) produced by the inertial sensor 6 inresponse to the read signal V_(S) and to the rotation of the gyroscope100. The preamplifier 134 and the sampler 135 are cascaded to the chargeamplifier 133, for processing the detection charge packets Q_(RS1),Q_(RS2) (converted into voltage by the charge amplifier 133) andgenerating the output signal S_(OUT).

As previously explained, the detection charge packets Q_(RS1), Q_(RS2)are generated by the inertial sensor 6 in response to the excitation ofthe detection mass 108 by the read signal V_(S) and are proportional tothe capacitive unbalancing of the second detection capacitances 122.This capacitive unbalancing is determined also by the amplitude of theread signal V_(S), as well as by the forces acting on the detection mass108. Consequently, the charge transferred with the detection chargepackets Q_(RS1), Q_(RS2) is correlated, in particular proportionally, tothe amplitude of the read signal V_(S), which varies at the resonancefrequency ω_(R). In practice, use of the demodulation signal V_(DEM) andthe read signal V_(S) for exciting the detection mass 108 enables tocarry out demodulation operation. Consequently, signals derived from thevoltage conversion of the detection charge packets Q_(RS1), Q_(RS2) aresignals already shifted back to base band, because the amplitude of theread signal V_(S) varies at the resonance frequency ω_(R).Advantageously, demodulation is not to be performed by the processingline 132, which is thus simple to design and, moreover, requires fewercomponents with respect to the processing lines necessary inconventional gyroscopes. Both the overall encumbrance and the powerconsumption are thus improved. In particular, it is possible toeliminate a demodulator stage and complex auxiliary circuits, such asphase-locked-loop (PLL) circuits that would otherwise be indispensablefor synchronizing the operation of demodulation with the carrierfrequency, i.e., the resonance frequency ω_(R). The disclosed embodimentis advantageous also in the case where a PLL circuit is in any caseincluded in the feedback stage 111 of the driving circuit. In fact, aPLL circuit that is to drive a demodulator stage is complex becausedemodulator stages require not only for synchronization at the resonancefrequency ω_(R), but also other clock signals at higher frequencies, butin any case controlled on the basis of the resonance frequency ω_(R).The advantage is obviously more considerable if the driving circuit doesnot include a PLL stage, but is, for example, based upon a simpler peakdetector.

FIG. 6, in which parts that are the same as those illustrated above aredesignated by the same reference numbers previously used, shows agyroscope 100′ according to a second embodiment of the disclosure. Thegyroscope 100′ comprises the microstructure 102, a driving device 103′,and a reading device 104′.

The driving device 103′ is substantially identical to the driving device103 already described with reference to FIGS. 3 and 4, except that inthis case the subtractor circuit 112 is not present. In particular, thedriving device 103′ is connected to the microstructure 102 so as to forma driving feedback loop 105, including the driving mass 107. The drivingdevice 103′ exploits the driving feedback loop 105 to maintain thedriving mass 107 in self-oscillation along the first axis X at itsresonance frequency ω_(R).

The reading device 104′ is of the open-loop type and is configured forexecuting a so-called “single-ended” reading of the displacements of thedetection mass 108 along the second axis Y. In this case, in particular,the detection mass 108 is excited by two read signals V_(S1), V_(S2)180° out of phase with respect to one another (see also FIGS. 7 a, 7 b),which are supplied to respective second terminals 6 b of the inertialsensor 6. In response to the read signals V_(S1), V_(S2), the inertialsensor 6 generates detection charge packets Q_(RS), which are suppliedon the first terminal 6 a. The detection charge packets Q_(RS) areproportional to the capacitive unbalancing of the second detectioncapacitances 122, caused by the displacement of the detection mass 108along the second axis Y.

More precisely, the reading device 104 has two first inputs 104 a′,connected to the driving device 104 for acquiring respectivedemodulation signals V_(DEM1), V_(DEM2); a second input, connected tothe first terminal 6 a of the inertial sensor 6, for receiving thedetection charge packets Q_(RS); first outputs, connected to respectivesecond terminals 6 b of the inertial sensor 6 and issuing the readsignals V_(S1), V_(S2); and a second output 104 b″, which supplies anoutput signal S_(OUT), correlated to the angular velocity Ω of themicrostructure 102. In the embodiment described herein, the demodulationsignals V_(DEM1), V_(DEM2) are voltages, which coincide with detectionvoltages V_(RD1), V_(RD2) present on the outputs of the transimpedanceamplifier 110. As already mentioned, the detection voltages V_(RD1),V_(RD2) are sinusoidal, oscillate at the resonance frequency ω_(R), haveequal amplitude and are 180° out of phase.

The reading device 104″ further includes a read signal generator 130″,the phase generator 131, and a processing line 132′, including a chargeamplifier 133′, a preamplifier 134′ and a sampler 135′. Unlike theprocessing line 132 of FIG. 4, the components that form the processingline 132′ are of the one-input/one-output type.

The read signal generator 130′ is a sampler and has a clock input,connected to the phase generator 131 for receiving the clock signal CK(with clock period T_(CK)), and inputs forming respective first inputs104 a′ of the reading circuit 104′. In practice, then, the inputs areconnected to the outputs of the transimpedance amplifier 110 of thedriving device 103 and receive respective demodulation signals V_(DEM1),V_(DEM2). Outputs of the read signal generator 130′ are connected torespective second terminals 6 b of the inertial sensor 6 and supplyrespective read signals V_(S1), V_(S2). In particular, the read signalsV_(S1), V_(S2) are generated by sampling and amplification of respectivedemodulation signals V_(DEM1), V_(DEM2) and hence have the form ofsquare-wave signals of amplitude that varies in a sinusoidal way at theresonance frequency ω_(R), with a mutual phase offset of 180°, asillustrated in FIGS. 7 a, 7 b.

Also in this case, the demodulation is performed directly duringexcitation of the detection mass 108, by supplying read signals V_(S1),V_(S2) of variable amplitude in a sinusoidal way at the resonancefrequency ω_(R). The charge transferred with the detection chargepackets Q_(RS) is in fact proportional to the difference V_(S1)−V_(S2)between the read signals V_(S1), V_(S2), which is in turn a sinusoidalsignal of frequency equal to the resonance frequency ω_(R). Signalsderived from the voltage conversion of the detection charge packetsQ_(RS) are hence translated into base band as a result of the form ofthe read signals V_(S1), V_(S2) applied to the detection mass 108.Consequently, it is not necessary to include circuits dedicated to thedemodulation in the processing line 132′.

A portion of a system 200 according to an embodiment of the presentdisclosure is illustrated in FIG. 8. The system 200 can be used indevices, such as, for example, a palmtop computer (personal digitalassistant, PDA), a laptop or portable computer, possibly with wirelesscapability, a cell phone, a messaging device, a digital music reader, adigital camera or other devices designed to process, store, transmit orreceive information. For example, the gyroscope 100 can be used in adigital camera for detecting movements and carrying out imagestabilization. In other embodiments, the gyroscope 100 is included in aportable computer, a PDA, or a cell phone for detecting a free fallcondition and activating a safety configuration. In a furtherembodiment, the gyroscope 100 is included in a user interface activatedby movement for computers or videogame consoles.

The system 200 may include a controller 210, an input/output (I/O)device 220 (for example, a keyboard or a screen), the gyroscope 100, awireless interface 240 and a memory 260, either of a volatile ornonvolatile type, coupled to one another through a bus 250. In oneembodiment, a battery 280 can be used for supplying the system 200. Itis to be noted that the scope of the present disclosure is not limitedto embodiments having necessarily one or all of the devices listed.

The controller 210 may include, for example, one or moremicroprocessors, microcontrollers, and the like.

The I/O device 220 may be used for generating a message. The system 200may use the wireless interface 240 for transmitting and receivingmessages to and from a wireless-communication network with aradiofrequency (RF) signal. Examples of wireless interface may comprisean antenna, a wireless transceiver, such as a dipole antenna, eventhough the scope of the present disclosure is not limited from thisstandpoint. In addition, the I/O device 220 may supply a voltage thatrepresents what is stored either in the form of digital outputs (ifdigital information has been stored) or in the form of analoginformation (if analog information has been stored).

Finally, it is evident that modifications and variations may be made tothe microelectromechanical gyroscope and to the method described,without thereby departing from the scope of the present disclosure, asdefined in the annexed claims. In particular, it is possible to usesignals different from the first read voltages (outputs of thetransimpedance amplifier 110); in particular, the signals may beacquired in different points of the feedback loop 105, for examplewithin the feedback stage 111.

The various embodiments described above can be combined to providefurther embodiments. All of the U.S. patents, U.S. patent applicationpublications, U.S. patent applications, foreign patents, foreign patentapplications and non-patent publications referred to in thisspecification and/or listed in the Application Data Sheet, areincorporated herein by reference, in their entirety. Aspects of theembodiments can be modified, if necessary to employ concepts of thevarious patents, applications and publications to provide yet furtherembodiments.

These and other changes can be made to the embodiments in light of theabove-detailed description. In general, in the following claims, theterms used should not be construed to limit the claims to the specificembodiments disclosed in the specification and the claims, but should beconstrued to include all possible embodiments along with the full scopeof equivalents to which such claims are entitled. Accordingly, theclaims are not limited by the disclosure.

The invention claimed is:
 1. A device, comprising: a first mass; asecond mass coupled to the first mass to oscillate in response to thefirst mass; a driving circuit coupled to the first mass to form afeedback control loop and to maintain the first mass in oscillation at aresonance frequency; a reading circuit coupled to the second mass todetect displacements of the second mass; and a read signal generatorstructured to supply to the second mass at least one read signal thatvaries with the resonance frequency.
 2. The device of claim 1 whereinthe reading circuit is an open loop circuit.
 3. The device of claim 1wherein the read signal generator is coupled to the driving circuit toreceive a demodulation signal.
 4. The device of claim 3 wherein thedriving circuit includes a transimpedance amplifier and a subtractorcircuit, the subtractor circuit coupled to output signals of thetransimpedance amplifier to generate the demodulation signal.
 5. Thedevice of claim 4 wherein the read signal generator is timed to samplethe demodulation signal in an asynchronous way with respect to theresonance frequency.
 6. The device of claim 1 wherein the readingcircuit is capacitively coupled to the second mass.
 7. The device ofclaim 1 wherein the reading circuit includes a charge amplifier, apreamplifier, and a sampler.
 8. The device of claim 7 wherein the chargeamplifier is coupled to the second mass, the preamplifier is coupled tothe charge amplifier, and the sampler is coupled to the preamplifier. 9.The system of claim 1 wherein the reading circuit includes a chargeamplifier, a preamplifier, and a sampler.
 10. The system of claim 9wherein the charge amplifier is coupled to the second mass, thepreamplifier is coupled to the charge amplifier, and the sampler iscoupled to the preamplifier.
 11. A gyroscope, comprising: a first massconfigured to oscillate along a first axis; a second mass coupled to thefirst mass and configured to oscillate in response to the first mass; adriving circuit coupled to the first mass to form a feedback controlloop and to maintain the first mass in oscillation at a resonancefrequency; a reading circuit coupled to the second mass to detectdisplacements of the second mass with respect to a second axis; and aread signal generator structured to supply to the second mass at leastone read signal that varies with the resonance frequency.
 12. Thegyroscope of claim 11 wherein the reading circuit is an open loopcircuit that is capacitively coupled to the second mass.
 13. Thegyroscope of claim 11 wherein the read signal generator is coupled tothe driving circuit to receive a demodulation signal, the drivingcircuit including a transimpedance amplifier and a subtractor circuit,the subtractor circuit coupled to output signals of the transimpedanceamplifier to generate the demodulation signal.
 14. The gyroscope ofclaim 13 wherein the read signal generator is timed to sample thedemodulation signal in an asynchronous way with respect to the resonancefrequency.
 15. A system, including: a gyroscope including: a first mass;and a second mass coupled to the first mass to oscillate in response tothe first mass; a driving circuit coupled to the first mass to form afeedback control loop and to maintain the first mass in oscillation at aresonance frequency; a reading circuit coupled to the second mass todetect displacements of the second mass, the reading circuit including aread signal generator structured to supply to the second mass at leastone read signal that varies with the resonance frequency; and a controlcircuit coupled to the gyroscope, the driving circuit, and the readingcircuit.
 16. The system of claim 15 wherein the reading circuit is anopen loop circuit.
 17. The system of claim 15 wherein the read signalgenerator is coupled to the driving circuit to receive a demodulationsignal.
 18. The system of claim 17 wherein the driving circuit includesa transimpedance amplifier and a subtractor circuit, the subtractorcircuit coupled to output signals of the transimpedance amplifier togenerate the demodulation signal.
 19. The system of claim 18 wherein theread signal generator is timed to sample the demodulation signal in anasynchronous way with respect to the resonance frequency.
 20. The systemof claim 15 wherein the reading circuit is capacitively coupled to thesecond mass.